The Monoclonal Antibody CMV Retinitis Trial has, as its primary objective, the comparison of the safety and efficacy of Human Anti-CMV Monoclonal Antibody (MSL 109) plus active primary treatment versus matched placebo plus active primary treatment for both newly diagnosed and relapsed CMV retinitis in patients with AIDS. The 325 patient trial will use a two-stage group sequential design in which the results from 76 patients enrolled and evaluated in the first stage will trigger a review of the Policy and Data Monitoring Board to determine whether to proceed to the full recruitment goal as planned, modify the trial, or terminate the trial. The design variables for the first stage are change in CMV virologic load and time to progression of retinitis. The design variable for the overall trial is time to progression of retinitis. Additional outcome measures include mortality, adverse events, change in visual acuity, and change in visual fields.